I am going ahead and making this post, this is because, there has been a lot of the same question going around the "Coven" forum, in order to "Apply" to take over an existing coven, that has been placed in "Inactive", you must have been on this site (had an account) for three months minimum. Event then it is left up to Petrarca to decided who is best suited for the positions.
Petrarca, looks at forum, articles, and spells history, making sure you are knowledgeable enough to be in that position, reminding, that there could possibly be about a hundred other applicants trying to become the Priest/ess of that coven.
This doesn't mean bumbard him with messages, this means, work hard, show your knowledge, and maybe you will get picked. This doesn't mean you will though.
Now another thing that has been asked around a lot is, "How do I create my own coven," the simple answer is, you can't. Petrarca, locked the ability to do that, this is because we have enough covens as it is. You can choose through the variety of different covens Spells of Magic has produced throughout the years.